Clinical observation as well as some recent preliminary studies suggest that the regulation of thirst and vasopressin secretion may be abnormal in many patients with uncontrolled diabetes mellitus. The objectives of this study will be to determine if the regulation of thirst or vasopressin secretion is abnormal in uncomplicated diabetes mellitus and, if so, whether it is due to alterations in the osmoregulatory or baroregulatory systems. The approach will be to apply 3 types of stimuli - hypertonic saline infusion, hypertonic glucose infusion and head up tilting - and compare their effects on thirst and plasma vasopressin in diabetics and control subjects. At the same time, plasma sodium, osmolality and renin activity as well as arterial pressure also will be monitored to determine if abnormal changes in any of these established stimuli could account for the abnormal thirst or vasopressin response. Finally, these studies will be performed in the patients both with and without insulin therapy to determine if the disorders in thirst or vasopressin regulation are a consequence of the insulin deficiency per se or of some other feature of the disease.